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Full text of "Text Book Of Mechanical Engineering"

Appendix IV.                            963

CHAPTER X.

JP. 700. Electric Ignition for Gas and Oil Engines.

The advent of the motor car has brought electric firing into great
prominence, so that tube ignition has been practically abolished for
all types of engines. At the present time three systems of obtaining
the electric" spark are practically used : (i) the primary or the
storage battery, whose current pressure is intensified by means of
an induction coil, (2) a magneto-electric machine giving a current
of low pressure, (3) a small dynamo also producing a low-pressure
current.

The first of these systems may be illustrated by Fig. 898,
which shews the wiring adopted in the De Dion motors. Taking
the parts in order we have, A the battery, B the primary wires, in
circuit with the inner or primary winding p, j the induction coil
whose secondary winding s is coupled to the firing plug, the
current passing through the wire w and returning by the frame E
of the engine, and finally the make and break hammer M, also in
circuit with the primary winding. The battery consists either of
four Leclanche' dry cells giving about 6 volts at 3 to 10 amperes,
or of two to three storage cells of 2 volts each. The induction
coil consists of two windings, primary and secondary, as mentioned,
a soft iron core Q, and a condenser c made of layers of tinfoil and
waxed paper. The plug G being in place, the switch s is closed
and the engine shaft turned round, causing the cam H to rotate
also, which permits the hammer D to make and break contact at
the proper time, thus enabling the cell current to pass through the
induction coil, with the result that a secondary current of great
intensity but low amperage is created in the wire w, and the spark
passes at K, igniting the mixture in the cylinder. The ebonite
block L may be altered by a rod, as shewn dotted, so as to change
the firing position as regards the engine stroke, and this con-
stitutes a hand governor of great convenience, producing various
degrees of speed and power. The firing plug is shewn at N to a
larger scale, the wire and rod w w being insulated by porcelain,
and in some cases mica. The De Dion engine rotating at 1500
revolutions per minute does not permit of the attachment of a
trembling hammer to the induction coil, so the spark is produced